January 29, 2014

Austronesian (~1/3) Bantu (~2/3) admixture in Madagascar

Genome-wide evidence of Austronesian–Bantu admixture and cultural reversion in a hunter-gatherer group of Madagascar

Denis Pierron et al.

Linguistic and cultural evidence suggest that Madagascar was the final point of two major dispersals of Austronesian- and Bantu-speaking populations. Today, the Mikea are described as the last-known Malagasy population reported to be still practicing a hunter-gatherer lifestyle. It is unclear, however, whether the Mikea descend from a remnant population that existed before the arrival of Austronesian and Bantu agriculturalists or whether it is only their lifestyle that separates them from the other contemporary populations of South Madagascar. To address these questions we have performed a genome-wide analysis of >700,000 SNP markers on 21 Mikea, 24 Vezo, and 24 Temoro individuals, together with 50 individuals from Bajo and Lebbo populations from Indonesia. Our analyses of these data in the context of data available from other Southeast Asian and African populations reveal that all three Malagasy populations are derived from the same admixture event involving Austronesian and Bantu sources. In contrast to the fact that most of the vocabulary of the Malagasy speakers is derived from the Barito group of the Austronesian language family, we observe that only one-third of their genetic ancestry is related to the populations of the Java-Kalimantan-Sulawesi area. Because no additional ancestry components distinctive for the Mikea were found, it is likely that they have adopted their hunter-gatherer way of life through cultural reversion, and selection signals suggest a genetic adaptation to their new lifestyle.

Not too surprising. After all 1/3 and 2/3 isn't that different from early estimates of 50-50.

This could be a product of initial community structure (with an Austronesian seafarer population bringing more African Bantu farmers than their own number), or it could be a product early selection with Africans more resistant to diseases found in Madgascar and generally better adapted to local environments than Austronesians.

While language indicates that Austronesians had a cultural upper hand, it is also notable that this doesn't seem to have been decisive as evidenced by significant African admixture, Y-DNA and mtDNA proportions.

According to a number of amateur runs by Razib Khan, the Merina are approximently 30% African and 70% Austronesian while the other "highlander" group, the Betsileo are a little more than 40% African and 60% Austronesian. There doesn't seem to have been any sex-biased gene-flow in Madagascar.

Andrew there is no evidence of Bantu migrations across the Mozambique channel. It it probable that Arab slave traders brought them several hundred years after its colonization by Asians. Higher African birth rates likely fully account for the admixture.

I am not proposing that there were Bantu migrations across the Mozambique channel (there are actually slight traces of possible Mozambique DNA in Madagascar, but this could easily be recent in origin). The overwhelming evidence, instead, manifestly demonstrates that Bantu migration to Madgascar was from the East African coast to Madgascar.

The most plausible means for this to happen would be with boats built and operated by Austronesians whose maritime skills were unparalleled at the time particularly outside of the line of sight from land. There is no evidence to support the involvement of maritime Arab slave traders and the evidence that we do have generally disfavors this scenario.

The evidence for a relatively cooperative Austronesian facilitated migration without Arab slave trader involvement includes: (1) highly integrated society of Bantu and Austronesian individuals without evidence of sex biased gene flow (inconsistent with a slavery model), (2) a complete absence of Arab genetic traces in Madgascar's populations - the only non-African, non-Austronesia genetics in Madgascar are a slight amount of ancestry traceable to the East Coast of India, (3) a surprising dearth of material culture to provide evidence of Arab trade with Madagascar in either Madgascar or in Arabia until a very late date despite the fact that such objects would be highly distinctive, (4) the lack of Arabic or Swahili loan words in Madagascar's language, and (5) the lack of an African creole (which develops when you have a slave population that does not share a language with a slave owner population) in Madagascar.

@Andrew Anyone sailing from Dar es Salaam to say Diego Suarez - the northernmost point on Madagascar - of necessity crosses the Mozambique Channel by accepted geographic delineation. I never mentioned Mozambique as you have.Neither did I imply an Arab presence on the island.It is clear historically that the Arabs were not particularly interested in 'colonizing'southern territories, eg. the sultanate on Mayotte was only established in 1500.Until the 1860's the Sultan of Oman was exporting slaves from Dar es Salaam. To suggest the "assisted passage" of Bantu to Madagascar was not in fact part of an established trade in slaves remains unproven in my opinion.

Furthermore 'sex-biased gene flow' is neither a necessity nor prerequisite for the sale or delivery of slaves.

I beg to differ. The history of the island is complex. It was first settled by non bantu african hunter gatherers 4000BP. They must not have been a large population. Then came the austronesians but it is difficult to see if they were already admixed or admixure happened after arrival. What is certain is that there were two admixture events. One which occurred at the beggining of malagasy history and forms the base on which the island's populations are derived and a later slower admixture from later african migrants which tends to distinguish the different populations of the island.

The merina at the moment are unknown. Razib only tested one merina individual for autosomnal dna.

There definately was sexually biased geneflow on the island with bias towards bantu males and austronesian females. This is true all over the island with even the Merina having over 50% bantu y chromosomes. If you can present a model that is consistent qith these observations, I would like to hear it.

Classic explanations for a sex-biased selection in favor of Bantu males and Austronesian females is that of an external Bantu conquest of a native Austronesian population. You see this model used in, for example, explanations for the Aryan diffusion in India, though there it's helped by caste data not available in the Madagascar case. Such a model is sure to ruffle feathers among those who are subconsciously biased against the idea that Africans ever ruled over other peoples, especially the sophisticated Austronesian seafarers who were capable of traveling thousands of miles of ocean. But fair is fair; the model is not inapplicable here.

Another explanation, amenable to the sensibilities of those who want to forego a conquest scenario in the case of Madagascar, is simple sex based selection, whether during the migration / after it. In the former case, the Austronesian migrants, centuries after the migration, had a balanced population, while the new Bantu migrants were overwhelmingly male. The result of intermarriage then logically created a population high on Bantu male DNA, but low on Bantu female DNA, and vice versa for Austronesians, under egalitarian breeding conditions ie minimal out group discrimination, ie equal access of males from both groups to females from both groups. Such a scenario ought to go well with liberal optimists.

I'm reluctant to accept that the Mikea are simply the product of "cultural reversion," as suggested in this paper, based on a sample of only 21 Mikea genotypes. If the "hunter-gatherer way of life" of the Mikea were based solely on "a recent cultural reversion," as they infer, that does not explain their music, which is distinctly different from that of other Madagascar groups, and in fact, much closer to the music of African Pygmies and Bushmen, especially in their use of both hocketing and yodel. This, coupled with their hunter-gatherer economy strongly suggests that, culturally at least, they do probably represent an aboriginal African population which existed on the island prior to the Austronesian immigration.

This doesn't mean that the genetic findings are necessarily wrong, since there has been plenty of time for Mikea individuals to co-habit with mainstream Malagasies -- without necessarily giving up certain elements of their traditional culture. Genetics can be a useful clue, but not necessarily the last word.

I'm surprised to see Roger Blench's name in the list of authors, since he is among the few musicologists who, like myself, have recognized this very distinct aspect of Mikea culture.

For more on this issue, including a reference to, and discussion of, Blench's research on the Mikea, and his findings, which conflict with the findings in this paper, see http://music000001.blogspot.com/2007/07/63-power-of-music-1-case-of-mikea.html

I am pure Malagasy. My mother looks more Asian, my father looks like a Jew, and I look like the mixture of asian-arab-african genes in my face. I'm not the only one who look like this. My mom's sister looks like an Indian, her husband like a mixture of Afro and Asian, their children look like adopted all around asian continent. And we are pure Malagasy.This is because our African, Asian and Arab admixture was so perfect. You can yellow with afro hair and your son brown with straight hair. it's not surprising for us. Same with our language, we may have very different features, have many dialects, we always understand each other.There's also the funny fact Malagasy can recognize each other when travelling outside. It's 90 percent accurate.About the Mikea: they are a group of highlanders who never accepted the invasion of Europeans so decided to withdraw in the bush and hunt to live. Their dialect is pretty close to Center group dialect though they are in the South.

To find/discover a probable interesting correlation of genome investigation with the history of Madagascar, I would suggest that you take samplings out of the Protestant church, the Catholic church, and the Muslim mosque.I am amazed to read what a "pure and perfect" Malagasy is. Well, it's an opinion. I think a pure Bantu or a pure Malay descent in Madagascar can also claim to be a perfect Malagasy. It's right; the former President Andry Rajoelina is heavily Austronesian by his look. But the most important for France - who is actually governing Madagascar - is that he can claim to be a descent of the Gauls, though that is kept silent. On the other hand, the new President could have faced a little problem for being slightly Bantu, but that was fixed. He got another wife with an heavily Austronesian look as soon as it was planed that he is going to be the new President.

To find/discover a probable interesting correlation between the genome investigation and the history of Madagascar, I would suggest that you do the samplings out of a Protestant church, a Catholic church, and a Mosque. The look of the former President Andry Rajoelina happens to be heavily Austronesian. However, he is far to be trusted by the Merina because he actually is a French descendant, and his honesty is questionned for keeping that silent. By the way, for France who practically rules Madagascar, the « Pure and Perfect Malgache » is anybody who can chant that « nos ancêtres sont les Gaulois ! », no matter what the other biological admixtures are.The new President could have faced a little problem for looking slightly Bantu ( ? %), but that was fixed. As soon as it was planed that he is going to be the next President, he got another wife who has an heavily Austronesian style. Having an ethnically balanced government is believed to be crucial for Madagascar. I am afraid that we may end up calling upon geneticists to certify the genomes set of each prospective minister before doing the math.

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